1. Field of the Invention
This invention relates generally to an apparatus for magnetically recording video and audio signals, such as may constitute a television signal, and more particularly is directed to improvements in the recording of the audio signal in such an apparatus.
2. Description of the Prior Art
In video tape recorders according to the prior art for recording a color television signal on a magnetic tape, the chrominance and luminance signal components which constitute the color video signal are separated, and the chrominance signal component has its carrier frequency converted to a relatively low value, while the luminance component frequency modulates a relatively high frequency carrier, whereupon the frequency-converted chrominance signal component and the high side band of the frequency-modulated luminance signal component (hereinafter simply referred to as the "FM luminance signal") are mixed or combined to form a composite color video signal which is recorded on a magnetic tape in successive, parallel record tracks extending obliquely in respect to the longitudinal or running direction of the magnetic tape. In such existing system for recording a color television signal, the audio signal thereof is recorded on the magnetic tape in record tracks which extend in the longitudinal direction, that is, the running direction of the magnetic tape, and are hereinafter referred to simply as "audio tracks".
In the above described recording system of the prior art, the oblique or slant tracks which are skewed relative to the tape and in which the composite color video signal, comprised of the frequency-converted chrominance signal component and the frequency-modulated luminance signal component, is recorded, are formed by first and second substantially diametrically opposed rotary magnetic heads both supplied with the composite color video signal and alternately scanning the magnetic tape along a path at an angle to the longitudinal direction in which the tape is transported. In order to increase the recording density of the color video signal on the tape and thereby increase the duration of the recording, it has been known to restrict the speed at which the magnetic tape is transported during recording so that the successive slant tracks scanned by the rotary magnetic heads will be closely or immediately adjacent to each other, that is, so that spaces or so-called guard band between the adjacent slant tracks will be eliminated. However, in such case, the problem of "cross talk" arises in the reproducing or playback mode of the apparatus. In other words, during reproducing or playback, a transducer or head scanning one of the slant tracks for reproducing the composite color video signal recorded therein will also pick up or reproduce signals or cross talk from the next adjacent tracks.
The problem of cross talk has been substantially solved, at least in respect to the relatively high frequency frequency-modulated luminance signal component of the recorded composite color video signal, by providing the first and second rotary magnetic heads with different azimuth angles so that the composite color video signal will be recorded in each slant track by means of a magnetic head having an azimuth angle different from the azimuth angle of the head with which the composite color video signal is recorded in the next adjacent tracks. Thereafter, during reproducing or playback, each slant track is scanned by a rotary magnetic head having the corresponding azimuth angle with the result that a substantial azimuth loss is experienced as to the relatively high frequency components of the cross talk from the adjacent tracks. Thus, the cross talk in respect to the frequency-modulated luminance signal component is substantially suppressed.
However, the azimuth loss effect is rather poor in respect to the low frequency band of the cross talk, that is, in respect to the frequency-converted chrominance signal component, so that other measures need to be taken for eliminating or minimizing the low-frequency component of the cross talk. For example, as disclosed in detail in U.S. Pat. No. 4,007,482, issued Feb. 8, 1977, and having a common assignee herewith, cross talk in respect to the frequency-converted chrominance signal situated in a relatively low frequency band is substantially eliminated by recording the chrominance signal component with different first and second carriers in the adjacent tracks, respectively. Such first and second carriers modulated by the chrominance signal component recorded in adjacent tracks, respectively, may be distinguished from each other by their respective frequency and/or polarity characteristics so that, upon reproduction of the signal recorded in a particular track, the low frequency band of the cross talk from the tracks next adjacent thereto can be conveniently suppressed or eliminated by reason of the different frequency and/or polarity or phase characteristics of the respective carriers.
In the above described system for recording and reproducing a color television signal, each of the audio signals thereof, for example, the left and right stereophonic sound signals, is supplied to a respective fixed head which is continuously in contact with the magnetic tape adjacent a longitudinal edge of the latter so that the left and right stereophonic sound signals are respectively recorded in audio tracks extending longitudinally along the magnetic tape.
It will be appreciated that, when high density recording of the color video signal in successive slant tracks on the tape is effected as described above, the rotational speed of the rotary magnetic heads may be relied upon to provide the desired relatively high speed of each rotary magnetic head in respect to the magnetic tape for ensuring high quality recording of the color video signal in the slant or skewed tracks. However, for achieving the high density recording of the color video signal, the transport speed of the magnetic tape is necessarily quite low, for example, about 1.33 cm/sec. Thus, the relative velocity between the magnetic tape and the fixed heads which record the audio signals in the respective audio tracks is quite low with the result that the quality of the audio recording is deteriorated.
In order to solve the above problem associated with the recording of the audio signals, it has been proposed that the audio signals be frequency-modulated and then mixed with the composite color video signal to provide a mixed or combined signal supplied to the rotary magnetic heads for recording by the latter in the slant tracks. Although the foregoing proposal ensures that the relative speed of the rotary magnetic heads in respect to the magnetic tape will be sufficient to ensure that the recording quality of the audio signals will not be deleteriously affected by an inadequate head-to-tape speed, the reproduced audio signals are still of insufficient quality. More particularly, in the existing proposal for recording frequency-modulated audio signals along with the composite color video signal in the slant tracks on the magnetic tape, the frequency-modulated audio signals recorded in the next adjacent tracks have the same carrier frequency. Therefore, each audio signal reproduced from a particular track contains a zero beat interference due to the audio component of the cross talk from the adjacent tracks even though the level of such cross talk may be somewhat reduced by the previously mentioned azimuth loss.
Further, when frequency-modulated audio signals are recorded with the composite color video signal in the slant tracks on the magnetic tape, there is a danger that, if the levels of the recorded frequency-modulated audio signals are sufficient to provide an adequate S/N ratio, a beat or interference will occur between such audio signals and the luminance and chrominance components of the composite color video signal. Moreover, such problem of possible beating or interference between the frequency-modulated audio signals and the composite color video signal, and particularly the frequency-converted chrominance signal thereof, is accentuated when the head or heads and magnetic record medium have a magnetic characteristic varying with frequency.